This chapter focuses on convergence and parallel paths, primarily discussing their interaction with routing metrics and distances.
Convergence is the process routers go through when a route (network) or group of routes has become unavailable due to a link going down in the network or extreme packet loss on a link. This loss results in the routers flushing the lost routes and listening to see whether other routes are available. Routers usually store only the best route to a network in their routing tables. Other, higher-cost, routes may exist, but the router ignores them if it believes that the better route still exists.
In the example in Figure 2-1, RouterA converges on a new path to 168.71.8.1 because the link between RouterA and RouterC has failed.